In a Long Term Evolution (LTE) system, user equipment (UE) may establish a connection and synchronize an uplink with a cell using a random access procedure. The UE may perform uplink transmission only after the uplink has been synchronized.
Similarly, in a machine-to-machine (M2M) system, UE may also require a random access procedure to establish a connection and complete uplink synchronization.
Slightly different from the LTE system, there is a random access reject message in the M2M system in addition to a random access response message. As shown in FIG. 1, after receiving a random access request (Random Access Request) message sent by UE, an evolved NodeB (eNB) may notify, using a random access response (Random Access Response) message, the UE of access, or may reject UE access by sending a random access reject (Random Access Reject) message, and may tell the UE to wait for a period of time and then re-initiate a random access procedure. Both messages may be sent on a physical downlink control channel (PDCCH).
Generally, there is a huge quantity of UEs in a M2M system. For example, a monitoring network may include tens of thousands of monitoring nodes. Within a period of time, there may be a large quantity of nodes that initiate random access, and random access response or reject messages may be sent on PDCCHs. In addition, PDCCH resources may also be used for sending a scheduling message or a paging message. As a result, the PDCCH resources may become limited.
For example, in some emergency scenarios such as a fire warning, many UEs may detect an emergency. For example, when a fire breaks out, a large quantity of UEs may initiate a random access procedure within a short period of time, and an evolved NodeB (eNB) may need to send random access response or reject messages to these UEs on PDCCHs based on a network load status. In a case such as this, the PDCCHs may become even more limited than described above.
In conclusion, in a current wireless communications system such as the M2M system, control channels may become limited when random access procedures initiated by a plurality of terminal devices need to be processed within a short period of time.